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F-37

TROUBLESHOOTING & REPAIR

F-37

ABNORMAL OPEN CIRCUIT VOLTAGE - DC TIG MODE

ONE OUTPUT SCR NOT FUNCTIONING

CAUTION

HIGH VOLTAGE / HIGH FREQUENCY can damage test equipment.

Perform all voltage and waveform checks with high frequency circuit OFF.

Perform High Frequency Disable Procedure.

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50 V

This is NOT the typical DC (+) output voltage waveform. One output SCR is not function- ing. Note the “gap”in the waveform. One SCR gate was disconnected to simulate an open or non-functioning output SCR. Note that each vertical division represents 50 volts and that each horizontal division repre- sents 2 milliseconds in time.

Note: Scope probes connected at machine

output terminals: (+) probe to electrode, (–) probe to work.

0 V

2 ms

SCOPE SETTINGS

Volts/Div

50 V/Div.

Horizontal Sweep

2 ms/Div.

Coupling

DC

Trigger

Internal

 

 

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PRECISION TIG 185

Page 75
Image 75
Lincoln Electric SVM169-A service manual 50 V/Div